New llc option pie-copy-relocations to optimize access to extern globals.

This option indicates copy relocations support is available from the linker
when building as PIE and allows accesses to extern globals to avoid the GOT.

Differential Revision: https://reviews.llvm.org/D24849

llvm-svn: 284160

5 files changed, 129 insertions, 5 deletions

diff --git a/llvm/include/llvm/MC/MCTargetOptions.h b/llvm/include/llvm/MC/MCTargetOptions.h
index fd4c6e4e4fb..21091b378f8 100644
--- a/llvm/include/llvm/MC/MCTargetOptions.h
+++ b/llvm/include/llvm/MC/MCTargetOptions.h
@@ -41,6 +41,7 @@ public:
   bool MCSaveTempLabels : 1;
   bool MCUseDwarfDirectory : 1;
   bool MCIncrementalLinkerCompatible : 1;
+  bool MCPIECopyRelocations : 1;
   bool ShowMCEncoding : 1;
   bool ShowMCInst : 1;
   bool AsmVerbose : 1;
@@ -67,6 +68,7 @@ inline bool operator==(const MCTargetOptions &LHS, const MCTargetOptions &RHS) {
           ARE_EQUAL(MCSaveTempLabels) &&
           ARE_EQUAL(MCUseDwarfDirectory) &&
           ARE_EQUAL(MCIncrementalLinkerCompatible) &&
+          ARE_EQUAL(MCPIECopyRelocations) &&
           ARE_EQUAL(ShowMCEncoding) &&
           ARE_EQUAL(ShowMCInst) &&
           ARE_EQUAL(AsmVerbose) &&
diff --git a/llvm/include/llvm/MC/MCTargetOptionsCommandFlags.h b/llvm/include/llvm/MC/MCTargetOptionsCommandFlags.h
index 801dd6a2d50..cb020845801 100644
--- a/llvm/include/llvm/MC/MCTargetOptionsCommandFlags.h
+++ b/llvm/include/llvm/MC/MCTargetOptionsCommandFlags.h
@@ -38,6 +38,8 @@ cl::opt<bool> IncrementalLinkerCompatible(
         "When used with filetype=obj, "
         "emit an object file which can be used with an incremental linker"));
 
+cl::opt<bool> PIECopyRelocations("pie-copy-relocations", cl::desc("PIE Copy Relocations"));
+
 cl::opt<int> DwarfVersion("dwarf-version", cl::desc("Dwarf version"),
                           cl::init(0));
 
@@ -62,6 +64,7 @@ static inline MCTargetOptions InitMCTargetOptionsFromFlags() {
       (AsmInstrumentation == MCTargetOptions::AsmInstrumentationAddress);
   Options.MCRelaxAll = RelaxAll;
   Options.MCIncrementalLinkerCompatible = IncrementalLinkerCompatible;
+  Options.MCPIECopyRelocations = PIECopyRelocations;
   Options.DwarfVersion = DwarfVersion;
   Options.ShowMCInst = ShowMCInst;
   Options.ABIName = ABIName;
diff --git a/llvm/lib/MC/MCTargetOptions.cpp b/llvm/lib/MC/MCTargetOptions.cpp
index 1d956a8ffce..e847a17dfec 100644
--- a/llvm/lib/MC/MCTargetOptions.cpp
+++ b/llvm/lib/MC/MCTargetOptions.cpp
@@ -16,7 +16,8 @@ MCTargetOptions::MCTargetOptions()
     : SanitizeAddress(false), MCRelaxAll(false), MCNoExecStack(false),
       MCFatalWarnings(false), MCNoWarn(false), MCSaveTempLabels(false),
       MCUseDwarfDirectory(false), MCIncrementalLinkerCompatible(false),
-      ShowMCEncoding(false), ShowMCInst(false), AsmVerbose(false),
+      MCPIECopyRelocations(false), ShowMCEncoding(false),
+      ShowMCInst(false), AsmVerbose(false),
       PreserveAsmComments(true), DwarfVersion(0), ABIName() {}
 
 StringRef MCTargetOptions::getABIName() const {
diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
index 43a587ba847..792280af84d 100644
--- a/llvm/lib/Target/TargetMachine.cpp
+++ b/llvm/lib/Target/TargetMachine.cpp
@@ -115,9 +115,6 @@ static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
   llvm_unreachable("invalid TLS model");
 }
 
-// FIXME: make this a proper option
-static bool CanUseCopyRelocWithPIE = false;
-
 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
                                          const GlobalValue *GV) const {
   Reloc::Model RM = getRelocationModel();
@@ -154,8 +151,10 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
       return true;
 
     bool IsTLS = GV && GV->isThreadLocal();
+    bool IsAccessViaCopyRelocs =
+        Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
     // Check if we can use copy relocations.
-    if (!IsTLS && (RM == Reloc::Static || CanUseCopyRelocWithPIE))
+    if (!IsTLS && (RM == Reloc::Static || IsAccessViaCopyRelocs))
       return true;
   }
 
diff --git a/llvm/test/CodeGen/X86/global-access-pie-copyrelocs.ll b/llvm/test/CodeGen/X86/global-access-pie-copyrelocs.ll
new file mode 100644
index 00000000000..5c4a87c969c
--- /dev/null
+++ b/llvm/test/CodeGen/X86/global-access-pie-copyrelocs.ll
@@ -0,0 +1,119 @@
+; RUN: llc < %s -march=x86-64 -mcpu=generic -mtriple=x86_64-linux-gnu -relocation-model=pic -pie-copy-relocations \
+; RUN:   | FileCheck -check-prefix=X64 %s
+; RUN: llc < %s -emulated-tls -march=x86 -mcpu=generic -mtriple=i386-linux-gnu -relocation-model=pic -pie-copy-relocations \
+; RUN:   | FileCheck -check-prefix=X32 %s
+
+; External Linkage
+@a = global i32 0, align 4
+
+define i32 @my_access_global_a() #0 {
+; X32-LABEL: my_access_global_a:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl a@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_a:
+; X64:       movl a(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @a, align 4
+  ret i32 %0
+}
+
+; WeakAny Linkage
+@b = weak global i32 0, align 4
+
+define i32 @my_access_global_b() #0 {
+; X32-LABEL: my_access_global_b:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl b@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_b:
+; X64:       movl b(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @b, align 4
+  ret i32 %0
+}
+
+; Internal Linkage
+@c = internal global i32 0, align 4
+
+define i32 @my_access_global_c() #0 {
+; X32-LABEL: my_access_global_c:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl c@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_c:
+; X64:       movl c(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @c, align 4
+  ret i32 %0
+}
+
+; External Linkage, only declaration.
+@d = external global i32, align 4
+
+define i32 @my_access_global_load_d() #0 {
+; X32-LABEL: my_access_global_load_d:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl d@GOTOFF(%eax), %eax
+; X64-LABEL: my_access_global_load_d:
+; X64:       movl d(%rip), %eax
+
+entry:
+  %0 = load i32, i32* @d, align 4
+  ret i32 %0
+}
+
+; External Linkage, only declaration, store a value.
+
+define i32 @my_access_global_store_d() #0 {
+; X32-LABEL: my_access_global_store_d:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32-NEXT:  movl $2, d@GOTOFF(%eax)
+; X64-LABEL: my_access_global_store_d:
+; X64:  movl $2, d(%rip)
+
+entry:
+  store i32 2, i32* @d, align 4
+  ret i32 0
+}
+
+; External Linkage, function pointer access.
+declare i32 @access_fp(i32 ()*)
+declare i32 @foo()
+
+define i32 @my_access_fp_foo() #0 {
+; X32-LABEL: my_access_fp_foo:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %ebx
+; X32-NEXT:  movl	foo@GOT(%ebx), %eax
+; X64-LABEL: my_access_fp_foo:
+; X64:       movq foo@GOTPCREL(%rip), %rdi
+
+entry:
+  %call = call i32 @access_fp(i32 ()* @foo)
+  ret i32 %call
+}
+
+; LinkOnceODR Linkage, function pointer access.
+
+$bar = comdat any
+
+define linkonce_odr i32 @bar() comdat {
+entry:
+  ret i32 0
+}
+
+define i32 @my_access_fp_bar() #0 {
+; X32-LABEL: my_access_fp_bar:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %ebx
+; X32-NEXT:  leal	bar@GOTOFF(%ebx), %eax
+; X64-LABEL: my_access_fp_bar:
+; X64:       leaq bar(%rip), %rdi
+
+entry:
+  %call = call i32 @access_fp(i32 ()* @bar)
+  ret i32 %call
+}
+
+!llvm.module.flags = !{!0, !1}
+!0 = !{i32 1, !"PIC Level", i32 1}
+!1 = !{i32 1, !"PIE Level", i32 1}